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首页> 外文期刊>Biochemistry >Determination of the b820 subunit size of a bacterial core light-harvesting complex by small-angle neutron scattering.
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Determination of the b820 subunit size of a bacterial core light-harvesting complex by small-angle neutron scattering.

机译：小角度中子散射法测定细菌核心集光复合体的b820亚基大小。

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摘要

The B820 subunit is an integral pigment-membrane protein complex and can be obtained by both dissociation of the core light-harvesting complex (LH1) in photosynthetic bacteria and reconstitution from its component parts in the presence of n-octyl beta-d-glucopyranoside (OG). Intrinsic size of the B820 subunit from Rhodospirillum rubrum LH1 complex was measured by small-angle neutron scattering in perdeuterated OG solution and evaluated by Guinier analysis. Both the B820 subunits prepared by dissociation of LH1 and reconstitution from apopolypeptides and pigments were shown to have a molecular weight of 11 400 +/- 500 and radius of gyration of 11.0 +/- 1.0 A, corresponding to a heterodimer consisting of one pair of alphabeta-polypeptides and two bacteriochlorophyll a molecules. Molecular weights of micelles formed by OG alone in solutions were determined in a range from 30 000 to 50 000 over concentrations of 1-5% (w/v), and thus are much larger than that of the B820 subunit. Similar measurement on the pigment-depleted apopolypeptides revealed highly heterogeneous behavior in the OG solutions, indicating that aggregates with various sizes were formed. The result provides evidence that bacteriochlorophyll a molecules play a crucial role in stabilizing and maintaining the B820 subunits in the dimeric state in solution. Further measurements on individual alpha- and beta-polypeptides exhibited a marked difference in aggregation property between the two polypeptides. The alpha-polypeptides appear to be uniformly dissolved in OG solution in a monomeric form, whereas the beta-polypeptides favor a self-associated form and tend to form large aggregates even in the presence of detergent. The difference in aggregation tendency was discussed in relation to the different behavior between alpha- and beta-polypeptides in reconstitution with bacteriochlorophyll a molecules.
机译：B820亚基是必不可少的色素膜蛋白复合物，可以通过在光合细菌中解离核心光捕获复合物（LH1）以及在存在正辛基β-d-吡喃葡萄糖苷的情况下从其组成部分重构而获得（ OG）。通过在氘化OG溶液中的小角中子散射测量来自红红螺旋体LH1复合体的B820亚单位的内在大小，并通过Guinier分析进行评估。由LH1解离并由脱辅基多肽和色素重构而制备的B820亚基均显示分子量为11400 +/- 500，回转半径为11.0 +/- 1.0 A，对应于由一对字母多肽和两个细菌叶绿素a分子。在浓度为1-5％（w / v）的情况下，由OG单独形成的胶束的分子量测定范围为30000至50000，因此比B820亚基的分子量大得多。对贫颜料的载脂肽的类似测量表明，在OG溶液中存在高度异质的行为，表明形成了各种大小的聚集体。该结果提供了证据，细菌叶绿素a分子在稳定和维持溶液中的二聚体状态的B820亚基中起着至关重要的作用。对单个α-和β-多肽的进一步测量显示出两种多肽之间聚集特性的显着差异。 α-多肽似乎以单体形式均匀地溶解在OG溶液中，而β-多肽更倾向于自缔合形式，甚至在存在去污剂的情况下也倾向于形成大的聚集体。讨论了与细菌叶绿素a分子重构α-和β-多肽之间的不同行为有关的聚集趋势的差异。

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